Politico, citing senior party officials, said the NRCC had kept details of the hack hidden from the party’s leadership, as well as its house members, saying it feared it would make it harder to find the culprit.

NRCC spokesman Ian Prior said: “The NRCC can confirm that it was the victim of a cyber intrusion by an unknown entity. The cybersecurity of the Committee’s data is paramount, and upon learning of the intrusion, the NRCC immediately launched an internal investigation and notified the FBI, which is now investigating the matter.”

He added: “To protect the integrity of that investigation, the NRCC will offer no further comment on the incident.”